class Solution:
    def stringHash(self, s: str, k: int) -> str:

        sm = 0
        result = ""
        for i, v in enumerate(s):

            sm += ord(v) - ord("a")
            if (i + 1) % k == 0:
                result += chr(sm % 26 + ord("a"))
                sm = 0
        return result
